This invention generally relates to intravascular catheters, such as balloon catheters used in percutaneous transluminal coronary angioplasty (PTCA).
PTCA is a widely used procedure for the treatment of coronary heart disease. In this procedure, a balloon catheter is advanced into the patient""s coronary artery and the balloon on the catheter is inflated within the stenotic region of the patient""s artery to open up the arterial passageway and thereby increase the blood flow there through. To facilitate the advancement of the catheter into the patient""s coronary artery, a guiding catheter having a preshaped distal tip is first percutaneously introduced into the cardiovascular system of a patient by the Seldinger technique through the brachial or femoral arteries. The guiding catheter is advanced until the preshaped distal tip of the guiding catheter is disposed within the ascending aorta adjacent the ostium of the desired coronary artery, and the distal tip of the guiding catheter is then maneuvered into the ostium. A balloon catheter may then be advanced through the guiding catheter into the patient""s coronary artery over a guidewire until the balloon on the catheter is disposed within the stenotic region of the patient""s artery.
The balloon is inflated to open up the arterial passageway and increase the blood flow through the artery. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilation but not over expand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In a large number of angioplasty procedures, there may be a restenosis, i.e. reformation of the arterial plaque in the dilated arterial region. To reduce the restenosis rate and to strengthen the dilated area, physicians now frequently implant an intravascular prosthesis called a stent inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the expanded stent is left in place within the artery.
A low profile, or a small leading outer diameter, is necessary to guide the catheter to the location of the lesion with as little damage to the patient""s body lumen as possible. During balloon manufacture, a polymeric tube is formed into a finished balloon having a desired outer diameter and length. The balloon is then placed on the catheter and bonded thereto. Such a manufacturing process may create a step increase in outer diameter from the catheter distal tip to the balloon. The step may create a higher profile, and cause damage and difficulty moving the catheter through the body lumen.
What has been needed is an improved method of forming a thin walled catheter balloon shaft.
The present invention is directed to a method and system for forming a medical device component having a section with a reduced wall thickness, and the component formed thereby. The method generally comprises rotating a medical device component while a material removal device is placed into contact with a section of the rotating medical device component, to thereby remove material from around the circumference of the section of the component. The material is removed to reduce the overall outer diameter of a section of the component, or form specific configurations such as a threaded section in which the wall thickness is reduced intermittently to thereby form threads. In one embodiment, the medical device component is a catheter balloon in which at least one of the proximal and distal shaft sections of the balloon is thinned according to the method of the invention. In another embodiment, the component is a polymeric tube. Although discussed primarily in terms of a balloon for a catheter, the invention should be understood to include other medical device components, including polymeric tubes useful in forming a distal tip or catheter shaft section of a catheter.
In one embodiment, a catheter balloon comprises a proximal end, a distal end, an expandable section, a proximal shaft section between the proximal end and the expandable section, a distal shaft section between the expandable section and the distal end, and an outer surface. In accordance with a method of the invention, the balloon is placed on a mandrel having a longitudinal axis. The mandrel is rotated around the mandrel longitudinal axis with the balloon on it. A material removal device is positioned to be in contact with an outer surface of at least a section of the rotating balloon to thereby remove balloon material therefrom. The method can also be used on polymeric tube to reduce wall thickness, or form specific configurations such as threaded sections. Such a use would be beneficial if a low profile is needed on a tip of a catheter, or at a junction between two polymeric tubes having similar outer diameters.
The invention is also directed to a medical device component such as a catheter balloon formed according to a method which embodies features of the invention. In one embodiment, the balloon has an expandable section with a wall thickness of about 0.0005 to about 0.002 inches, a distal shaft section having a wall thickness, reduced according to the invention, of about 0.001 to about 0.015 inches, more specifically about 0.002 to about 0.006 inches, and a proximal shaft section having a wall thickness, reduced according to the invention, of about 0.002 to about 0.015 inches, more specifically about 0.002 to about 0.006 inches. The wall thickness of the balloon shaft sections may be greater than or substantially equal to the wall thickness of the expandable section of the balloon. In one embodiment, the proximal shaft section has a wall thickness greater than or equal to the wall thickness of the distal section, and the distal shaft section wall thickness is greater than or equal to the wall thickness of the expandable section. In one embodiment, the shaft sections have a wall thickness about 3 to about 10 times greater than the wall thickness in the expandable section.
The method of the invention provides an improved medical device component having a section with a reduced wall thickness, due to the uniform removal of material. A balloon catheter having a balloon shaft section with a reduced wall thickness according to the invention has improved trackability and crossability. Moreover, the method of the invention does not negatively impact the balloon""s rupture and fatigue characteristics. The method of the invention provides for uniform material removal, which thus prevents or lessens the formation of weak spots in the balloon. A thinner wall at the balloon shaft or at a junction will allow for a more flexible transition area from balloon to catheter shaft, or from one polymeric tube to another. The process allows for a reliable, repeatable removal of material, and can be automated to allow for a low cost alternative to removing the material by hand.